Automatic control system for fuel burners



y 1943 .1. M. WILSON AUTOMATIC CONTROL SYSTEM FOR FUEL BURNERS Filed March 5, 1942 INVENTOR. 39 1101mm. M. Wilson...-

BY '51'. .3 ML.

A1 fanny" Patented May 18, 1943 AUTOMATIC CONTROL SYSTEM FOR FUEL BURNERS John M. Wilson, Minneapolis, Minn, assignor to Minneapolis-Honeywell Regulator Company, Minneapolis, Minn" a corporation of Delaware Application March 5, 1942, Serial No. 433,493

14 Claims.

This invention relates to an automatic control system for fluid fuel burners in which the system is put through its starting and stopping sequence by means or a control motor.

One of the main objects of this invention is to design a motor operated iuel burner control system which utilizes a minimum number of parts and which is simple in operation thus assuring a low production cost, while incorporating therein all of the necessary features of safety required in fuel burner control systems.

A further object of the invention is to design a control system of the abov type in which a control unit in the form of a plurality of cams is operated by a control motor to energize the fuel feeding device and ignition means and then open a safety switch and lock the system out in the event that combustion is not established within [the normal trial ignition period. A closed hot combustion switch is provided for preventing the opening of the safety switch in the event that combustion is established first, and the control motor then continues to operate until the control unit reaches a mnning position at which time it deenergizes the control motor.

Another object of the invention is to provide the system with a return switch so that the control motor will return to its original starting position upon the opening of the safety switch or when the room thermostat or other condition responsive device in control of the system is satisfled.

A still further object of the invention is to control the safety switch and return switch by the conjoint action of the control motor and an elmtromagnetic relay which is energized as long as there is a demand for burner operation. or upon a failure of ignition. Where the fluid fuel being controlled is oil and an oil valve is used in addition to the usual burner motor, it is also contemplated that the relay may control a switch in series w th the-oil valve so that this valve will he closed immediately upon the satisfaction of the emand for burner operation whereas the burner motor will remain energized until the control motor can operate the control unit sufficient y to open the switch in series with the burner motor. One of the chief advantages of this operation is that it g ves a short blow-out cycle and thus prevents oil dripping into the combustion chamber zfter the burner motor has been stopped.

A still further object of the invention is to utilize a single operating member for controlling the opening of the safety switch and also for closing and latching the return switch. This operating member is normally biased to a position where it prevents opening of the saiety switch and maintains the return switch in open position but is biased to its other position by the control unit when the control unit reaches an intermediate position which corresponds to the end of the trial ignition period and also when the control unit reaches its running position. This is so that the operating member may be biased to close the retm'n switch and release the safety switch for movement to open position in the event that combustion is not established at the end of the trial ignition period and so that this same operating member may close the return switch when the demand for burner operation has been satisfied and the control unit is in its running position. A separate means on the control unit prevents the operating member from opening the safety switch ate position corresponding to the end of the trial ignition period.

The invention further contemplates, where intermittent ignition is desired, that the burner motor and ignition device shall be brought on simultaneously when the control motor is started in response to a demand for burner operation and that the ignition device shall be deenergized be fore the control motor reaches its intermediate position so that the combustion responsive switch will he closed to prevent opening of the safety switch only if combustion has been well established.

These and other objects will readily become apparent as the following specification is read in the light of the accompanying drawing in which:

Figure 1 is a schematic wiring diagram of the circuit in which my invention is used,

Figure 2 is a more or less diagrammatic showing of my control motor, control unit, and switches operated thereby with the control unit being shown in starting position, and I Figure 3 is a view similar to Figure 2 with the control unit being shown in running position.

This application is directed to the same general type of system as my copending application, Serial No. 4335M which was filed concurrently herewith.

Referring first to Figure 2 of the drawing, the control motor it operates a control unit 6 8 through the reduction gearing E2. The control unit it comprises a rotatable shaft indicated by the dotted hue it, which shaft carries a plurality Ofcams i4, i5, l6, i1, l3, l9 and 2d.

The cams i4 and I5 are adapted to cooperate with the relay 2| in controlling the action of the return switch 22 and the safety switch 23. The return switch 22 comprises a pair of contact blades 25 and 25 which are biased to open circuit position as shown in Figure 2 of the drawing. The safety switch 23 comprises a pair of resilient contact blades 26 and 27, the blade 2'! being biased upwardly to open circuit position. A latch 23 pivoted at 29 normally holds the safety switch 23 latched in closed position as shown in Figure 2, but this latch is continuously biased to its tripped position by means of the spring 39. The latch 28 is provided with an extension 3i which cooperates with the surface of cam i so that this cam normally prevents the biasing spring 30 from moving the latch 28 to its tripped position,

except when the extension it enters into the low part 32 of cam I5.

An operating member 341 is pivotally mounted at 35 and. as shown in Figure 2, is biased by means, of the spring 36 into a first position in engagement with the stop pin 37. In this position a latching surface 38 en ages the end 39 of the latch 2a to prevent this latch from being moved to its tripped position by means of the spring 38.

The relay 29 is shown as having a pivoted armaengaging the roller :3 i, as shown in Figure 2. there is substantially no tension in the sprin fi l and therefore the weaker spring 3% is efiective to bias the operating member 33 into its first posi ion in engagement with the stop pin 3?. When the earn as is rotated far enough so that the high portion of the cam engages the roller :15, the lever 12 is rotated in a clockwise direction, tensioning the spring M. This sprin it is stronger than spring 36 and therefore its effect. when tensioned, is to overcome the spring 35 and bias the operating member 38 for rotation in a clockwise direct on to a second operating position. As long as the relay 2! is energized. its armature 39 prevents th clockwise rotation of the operating member 3 1 and it remains in the position shown in Figure 2. However. if the relay 2! should be deenereized. such clockwise rotation of the operating member 3 will be permitted.

This clockwise rotation of the operating member 33 removes the latchin surface 38 from the end 3? of the latch 28 so that if the extension 3! on this latch is opposite the. low point 32 of the cam 45. then the s ring 3B is operative torotate the latch 28 to its tripped position and permit the safety switch 23 to open. The safety switch 23 will then remain open until it is manually closed by the reset member 35.

Clockwise rotation of the operatina member 35' under the influence of the spring 33 will additionally cause this member to close. the return switch 22 and at the same time a latch member ll which is pivoted at #38 will drop down under the influence of its biasing spring 69 and latch the return switch 22 in closed position. This will occur whenever the return switch is closed and the return switch will then remain closed until the cam I5 has rotated sufficiently to cause its high point E6 to engage extension 5i on the latch 23, and the cams i l and it cooperate with relay ll and move this latch to its tripped position, as

2t to control the return switch 22.

For the sake of simplifying the drawing, the armature 3Q of the relay 2! and the operating member 34 have been shown in such a position that the tension of the spring Si will' tend to move the armature 39 to its deenergized position. Actually, the relay 2| is reversed and a member operated by the armature 39 slips in between the end 40 of the operating member 3% and the relay 2| so that the effect of the spring 35 is to tend to move the armature 39 towards its energized position. In this way it would never be possible for the spring 35 to bring the armature to its deenergized position. The diagrammatic showing, however, is thought to be operable and therefore suficient to show the operation of the system as a whole.

The control motor switch 56 is shown as comprising a pair of resilient contact blades 55 and 55 which are biased to open position as shown in Figure 3. An insulating member 5? carried by the free end of the resilient blade 55 cooperates with the surface of the cam i? so that when it engages the high surface of the cam, as shown in Figure 2, switch 54 is closed and when it engages the low surface of the cam, as shown in Figure 3. the switch 56 is opened.

The switches 69 and Si are shown as comprising the resilient contact blades 52, 53 and 86, the blades 52. and at being biased to their straight line positions whereas the blade 33 is shown as being biased to its upper position in Figure 2 in which it engages the blade 82 to close the switch $5. This takes place when the insulating member 65 carried by the free end of the blade 63 is in engagement with the lowest portion of the cam 58. When the cam rotates slightly in its clockwise direction the insulating member 8% is in engagement with the intermediate portion 56 of the cam it, at which time the blade 53 is moved downwardly until it engages the blade 63, the blade '62 remaining in engagement with blade 53 during this movement. When the highest portion of the cam it engages the insulating member 55, the blade 53 is in its lowest position in which the switch 5i is closed and the switch is open. This position is shown in Figure 3.

The burner motor switch 53 comprises a pair of resilient contact blades 59 and i8 which are biased to open circuit position as shown in Figure 2. When the insulating member ll carried by the blade HG engages the low portion of the cam i9, switch 88 is in open circuit position as shown in Figure 2, but when the insulating member Ii engages the high portion of the cam 99. switch 8% is closed as shown in Figure 3:

Ignition switch 32 comprises a pair of resilient contact blades 73 andfi i which are biased to open circuit positionas shownin Figure 3. When the insulating member '75 carried by the free end of the contact bladefl' engages the high point of cam 28, the switch'l2 is closed as shown in Figure 2, and when the insulating member 75 engages the low point of earn as switch 12 is open as shown in Figure 3.

The system shownvin Figure 1 is intended to respond to some condition which isindicative of a demand for burner operation. It will be appreciated that this may be any one of a number of different conditions, but for the purposes of illustration the condition chosen is dry bulb temperature. Therefore, a room thermostat 80 is utilized, this thermostat comprising a bimetallic element 8| having a resilient contact blade 82 and a second contact blade 83. On a decrease in temperature, the bimetallic element 8| is adapted to contract and first cause the resilient contact blade 82 to engage the stationary contact 88 and then cause the contact blade 83 to engage the stationary contact 85.

A reference numeral 88 indicates generally any one of a number of well known combustion responsive devices for positioning a-contact arm 81 into engagement with a cold contact 88 in the absence of combustion and into engagement with a hot contact 88 in the presence of combustion. It will be understood that this is not intended to be a calibrated switching device ut one which will respond to the appearance and disappearance of a flame at the burner. It is not necessary that this switching action overlap in either direction.

The relay 2| is shown as comprising an electric winding 88 and the armature 39 which, when the relay is energized, is adapted to move the relay arms QIR, 82R, and MR, into engagement with their stationary contacts 94, 95 and 88, respectively. The letter R" has been used after the reference numerals indicating the relay arms in order to indicate that these arms are actuated by the relay.

The control motor i8 is shown as having a rotor 98 and an energizingwinding 89. When a circuit is closed to the winding 99, it will be understood that the control motor 9 9 is energized to cause rotation of the rotor 98, which, through the reduction gearing I2, rotates the shaft 63 of the control unit ii. The switches 22, 23, 5t, 69. 6|, 5% and 32 which are controlled by the control unit are shown in Figure l in the same positions which they occupy in Figure 2.

This system is provided with the usual oil burner motor Hill and ignition device Hi. It is also provided with an electromagnetically operated oil valve E82 which, when deenergized, prevents the how of oil to the burner.

The electrical power for operating the system is obtained from the two supply lines it and IEI-t to which the primary winding tilt of a step-down transformer 5 or is connected by means of conductors IE3? and 988. The transformer IE5 videzl. with a secondary winding Hi9 which sup- ;clles power to the low voltage portion of the systom.

Qperation The various elements of the system are'shown in the position which they will occupy when the is procontrol unit is in its starting position and the temperature in the room being controlled has decreased sufficiently to cause the switch arm 83 to engage its stationary contact 85, this action occurring at a slightly lower temperature than that at which the resilient contact arm 82 engages its stationary contact 84. The closure of the two room thermostat switches results in the establishment of a circuit from one side of the secondary winding 899 through conductor H2, switch 23. conductor H3, contact 84, switch blades t2 and 83, stationary contact 85, conductors H4. H5 and I86, switch 68, conductor I ll, switch arm 81, cold contact 88, conductors I I8 and I I8, winding 98 of the relay 2 I, and conductor I20 back to the other side of the secondary winding I88. This circuit results in the energization of the relay 2| which then moves the relay arms 9| R, 82R, and 93R into engagement with their stationary contacts 84, 95 and 96, as shown in Figure l of the drawing. The engagement of the relay arm 8IR. with its stationary contact 94 establishes the usual holding circuit from one side of the secondary winding I08, through conductor II2, safety switch 23, conductor II3, contact 84, resilient switch blade 82, bimetallic element 8|, conductor I2I, relay arm SIR, stationary contact 84, conductors 22, H5 and H6, switch 68, conductor III, swimh arm 81, cold contact 88, conductors H8 and I I8, relay winding 88, and conductor I20 back to the other side of the secondary Winding I09. This holding circuit is therefore independent of the contact blade 83 and stationary contact of the room thermostat 88.

The engagement of the relay arm 82R with its stationary contact setsup a circuit for the control motor I8. This circuit extends from one side of the secondary winding I09 through conductor II2, safety switch 23, conductor H3, contact 84, resilient switch blade 82, bimetallic element 8|, conductor I 2|, relay arm SIR, contact 94, conductors I22, H5 and I24. contact 95, relay arm 92R, conductor I25, switch 54, conductors I26 and I27, energizing winding 99 for the control motor I II, and conductors I28 and I20 back to the other side of the secondary winding I09. Energization of the relay 2| therefore results in the energization of the control motor In which immediately starts to rotate the control unit II from its starting position in a clockwise direction, as seen in Figures 2 and 3.

As the control unit iI starts to rotate, the cam 89 will first cause the closure of the switch 68 which will result in the simultaneous energizetion of the oil valve 592, burner motor tee and ignition device E iii. The oil valve I or is energized by a circuit extending from the supply line let through conductor $29, switch conductors 23d and E35, relay arm contact $56, conductor E32, oil valve 32, and conductor it'd to the other supply line The burner motor will be energized by a circuit extending from the supply line E33 through conductor i29, switch conductors itil and i3 3, burner motor Mid, and conductor I35 back to the other supply line Hid. The ignition device will be energized from a circuit ex tending from the supply line let through conductor 52$, switch E38, conductors 536 and E38, switch 32, conductor i'l, ignition device Idi, and conductor i238 back to the other supply line I06.

The closure of the above three circuits normally results in the establishment of combustion at the burner. It will be noted that at substantially the same time as the cam i9 closes the switch S8 for energizing the oil valve, burner motor and ignition device, the cam to causes its intermediate surface 68 to engage the insulating portion 85 on the blade 63 and therefore causes this blade to move downwardly into engagement with the blade 6 resulting in the closure of the switch 6i while maintaining the switch S9 in closed position. This results in a holding circuit for the relay winding so which is independent of the combustion responsive switch arm 87 and the cold contact 88. This circuit extends from one side of the secondary winding I09 through conductor Hi2, safety switch 23, conductor 1 I3, contact 8d, resilient switch blade 82, bimetallic element 8!, conductor l2l, relay arm QlR, contact 98, conductors I22, H5 and H5, switches 6d and ti in series, conductors Hill and M9, relay winding 98, and conductor I back to the other side of the secondary winding ills. Therefore, if combustion is established'causing the combustion responsive switch arm 81 to separate from the cold contact 88, the relay winding 98 will nevertheless remain energized and the control motor ill will continue to operate.

The combustion responsive switch arm Bl in continued response to combustion will continue to move into engagement with the hot contact 89. This sets up a holding circuit for the relay winding 90 which is independent of the switch 88 through which the original energizing circuit for the relay winding 90 passed. The latter holding circuit may be traced from one side of the secondary winding Hi9 through conductor H2, safety switch 23, conductor H3, contact B l, resilient switchblade 82, bimetallic element d l, conductor l2l, relay arm SIR, contact 96, conductors I22, I15 and I26, contact 85, relay arm 9213., conductor Mil, hot contact 89, switch arm 8?, conductor Ill, switch 6|, conductors 8% and H9, relay winding 96, and conductor 526 back to the other side of the secondary winding 6839.

Continued rotation of the control unit it will cause the insulating member T15 of the ignition switch 22 to slip oil? the high side of the cam 26 thus resulting in the opening of the ignition switch B2. The control unit it is new approaching its intermediate position in which it will open the safety switch 23 in the event that combustion has not been established. Atthis time the cam it has rotated so that its highpoint Eli has released the latch Ill for operation by its biasing spring 89 in the event that the return switch it should be closed. The cam !5 has rotated until its lowpoint 32 is opposite the projection 311 on the latch 28 so that this latch may be moved by its biasing spring 38 to open the safety switch 23 in the event that the latch 28 is released by the operating member 38. The carn M has rotated sufficiently to rotate the lever 52 and tension the biasing spring a l to bias the operating member for rotation in a clockwise direction to cause it to release the latch 28 in the event that the relay 2! should be deenergized. At this same time, the cam 18 moves its high side into engagement with the insulating portion $5 on theswitch blade as so that this switch blade moves downwardly to open the switch all.

At this time the relay 2! will be deenergized if the combustion responsive switch arm 8? is not in engagement with its hot contact 89 but will remain energized by the holding circuit traced above through the hot contact 89 in the event that combustion has been established.

Let it be assumed first that combustion has not been established at this time and that the combustion responsive switch arm 81 is still in engagement with the cold contact 88. Opening of the switch 66 will therefore break; the circuit through the relay winding at and the relay 2! will become deenergized and drop out its armature 39. This permits the biasing spring M to rotate the operating membert i in a clockwise direction and release the latch 28, which in turn is rotated by its spring 38 to release the safety switch 28 for movement in open direction. Opening of the safety switch 23 breaks the original circuit to the control motor Id, but this motor is immediately reenergized because at the same time aaiaaeo ing of the safety switch 23 it closes and latches the, return switch 22. This latch is of course the latch kl? which moves downward into latched position by means of its biasing spring d9. Thus the control motor 58 immediately starts operating again.

The ignition let, it will be remembered, has already been deenergized, and the deenergization of the relay it results in the movement of the relay arm 93R to open circuit position which results in the immediate closure of the oil valve N32. The switch '68 is still closed however, and therefore the burner motor lflfi-continues to operate. The control unit H therefore rotates under th influence of the control motor l8 which is now energized by the return switch 22. This energizing circuit extends from one side of the secondary winding Hi9 through conductors 2, Hi5, return switch 22, conductors M8, in, energizing winding 99, and conductors H8 and 526 back to the other side of the secondary winding N39. The control motor IE will continue to operate until the control unit it has returned to its starting position, at which time the high point 50 on the cam l5 trips the latch fill and permits the return switch 22 to open. In this position of the control unit, th cam l i is in the position shown in Figure 2 in which it has released the tension of the biasing spring 66 with the result that the operating member 3% is now biased to its position against the stop pin 3i and will not reclose the return switch 22. The control motor will therefore be deenergized with the control unit in the starting position. At this time the cam l5 will have returned the latch 28 to its latched position but the safety switch 23 will remain open until it is manually reset on the resilient latching blade 33 carried by the latch 23. Moreover, the control motor lD cannot be reenergized until this safety switch 23 is reclosed due to the fact that this switch is in the thermostat circuit and therefore will maintain the circuit to the control motor it open even though the room thermostat 8G is closing both of its thermostatic switches in response to a demand for burner operation.

tion shown in Figures 1 and 2 of the drawing and the system will then go through a normal starting operation.

Let it be assumed now that the control unit it is in its intermediate position wherein the cam It has tensioned the biasing spring M, cam 55 has positioned its'low point 32 opposite projection 31 on the latch 23, high point 50 of cam it has moved to permit action of the latch d? by its biasing spring 59, switch 68 is closed by cam i9, and ignition switch 72 has been opened by cam 29, and the. cam It has just opened the switch 59. If at this time combustion has been established the combustion responsive switch arm 31 will b in engagement with its hot contact 89 and the relay EA will remain energized by means of a circuit extending from one side of the secondary winding 809 through conductor H2, safety switch 23, conductor H3, contact 3%, resilient switch blade 32, bimetallic element at, con

' ductor i2i, relay arm QlR, contact 96, conductors that the operating memberd l permits the openl22, H5, and 52! contact 95, relay arm 52R, conductor Mil, hot contact 89, combustion responsive switch arm 3?, conductor Ill, switch 6|, conductors M6 and H9, relay winding 90, and conductor l 20 back to the other side of the secondary winding I99. The armature 39 of the relay M will therefore not release the operating member When the safety switch; 23 is manually set, theparts will be in the posi- 34 for movement by the biasing spring 44 with the result that the safety switch 23 will remain closed and the return switch 22 will remain open. The control motor Ill will therefore remain in operation and the control unit II will continue to operate until the cam l7 moves its low portion adjacent the insulating member 51 which results in the opening of the switch 54. This breaks the circuit to the control motor iii and therefore deenergiziug it, although the relay 2! will still remain energized by the circuit just traced above. This is the normal running condition of the system in which the oil valve 102 is opened, burner motor Hid energized and the ignition lill deenergized.

With the control unit ii in its running position, ii the relay 2! is deenergized, either as a result of a failure of the flame at the burner or as a result of the room thermostat opening switch 82, 8d, the armature 39 will be released and permit the operating member 34 to rotate in a clockwise direction under the influence of its biasing spring 44. This results in the closure of the return switch 22 and the latching thereof by means of the latch 41. The control motor Ill will therefore be energized and will rotate the control unit ii back to its starting position, at which time the high point 50 on the cam 16 will trip the return switch to open position. The parts will then have returned to the positions shown in Figures 1 and 2 of the drawing.

It willbe noted that the motor control switch 54 always maintains energization of the control motor it! when it is operating normally until the control unit ll reaches its running position, at which tim the switch 54 opens and stops the motor in this position. The motor then remains deenergized until the return switch 22 is closed as a result of the deenergization of the relay 2|.

It will be noted further that whenever the relay Ei is deenergized for any reason the oil valve I02 is immediately closed due to the breaking of the circuit therethrough at the relay arm 93R. The burner motor I00, however, will continue in operation until the cam [9 opens the motor switch 88. This provides for a blow-out cycle.

Various changes and modifications of the invention will undoubtedly occur to those who are skilled in the art, and I therefore wish it to be understood that I intend to be limited by the scope of the appended claims and not by the specific embodiment disclosed which is for the purpose of illustration only.

I claim as my invention:

1. In a motor operated fuel burner control system, a control motor, a control unit operated thereby and having a starting position, an eleci tric device which, when energized, causes the delivery oi fuel to a burnena first switch in control of said device, said-first switch being operated by said control unit and open when said control unit is in starting position, a relay in control of said control motona circuit for said relay, a condition responsive element for closin said circuit, the resultant movement of said control unit from its starting position causing closure oi said first switch, switch means operated by said control unit for deenergizing said control motor when said control unit reaches a running position, a return switch for energizing said control motor independently of said switch means, means controlled by said relay upon deenergization thereof for closing said return switch, and means operated by said control unit when it reaches its starting position for opening said return switch, said first switch being opened by said control unit as it leaves its running position.

2. In a motor operated fuel burner control system, a control motor, a control unit operated thereby and having a starting position, an electric device which, when energized, causes the delivery of fuel to a burner, a first switch in control of said device, said first switch being operated by said control unit and open when said control unit is in startingposition, a relay in control of said control motor, a circuit for said relay, a condition responsive element for closing said circuit, the resultant movement of said control unit from its starting position causing closure or" said first switch, switch means operated by said control unit for deenergizing said control motor when said control unit reaches a running position, a normally open return switch for energizing said control motor independently of said switch means, a latch for latching said return switch in closed position, a member biased to a position in which it latches said return switch closed, said member being restrained by said relay when it is energized but permitting such latching operation when deenergized, and means operated by said control unit for removing the bias from said latching member and for tripping said return switch to open position when said control unit reaches its starting position.

3. In a motor operated oil burner control system, a control motor, a control unit operated thereby and having a starting position, an oil burner motor associated with an oil burner, an electrically operated oil valve for alternately cutting off and permitting the flow of oil to the burner, a relay in control of said control motor, a relay switch in series with said oil valve, a first switch in control of both said burner motor and oil valve, 9. condition responsive switching means for energizing said relay thus closing said relay switch and causing operation of said control motor, said control unitl closing said first switch as it is moved from its starting position by said control motor to energize simultaneously said burner motor and open said oil valve, means operated by said control unit :for stopping said for reenergizing said control motor, said oil valve closing immediately upon deenergization of said relay, said control unit opening said first switch as it moves from its starting position, and means operated by said control unit for opening said return switch when it reaches its starting position.

4. In a motor operated oil burner control system, a control motor, a control unit operated thereby and having a starting position, an oil burner motor associated with an oil burner, an electrically operated oil valve for alternately cutting ofi and permitting the flow of oil to the burner, means for igniting the fuel at the burner, a relay in control of said control motor, a relay switch in series with said oil valve, a first switch in control of said oil valve, burner motor and igniting means, a second switch in series with said igniting means, a condition responsive switching means for energizing said relay thus closing said relay switch and causing operation of said control motor, said control unit closing said first switch as it moves from its starting position, means operative by said control unit for closing said second switch before said first switch is closed whereby the opening of said oil valve and the energization of said burner motor and igniting means occur simultaneously, said control unit opening said second switch as it reaches an intermediate position, and then deenergizing said control motor as it reaches a running position, a return switch for said control motor, means controlled by said relay for closing said return switch upon deenergization thereof for reenergizing said control motor, said oil valve closing immediately upon deenergization of said relay, said control unit opening said first switch as it moves from its starting position, and means operated by said control unit for opening said return switch when its reaches its starting position.

5. In a motor operated fuel burner control system, a control motor, a control unit operated thereby and havin a starting position, an electric device which, when energized, causes the delivery of fuel to a burner, a first switch in control of said device, said first switch being operated by said control unit and open when said control unit is in starting position, a relay in control of said control motor, a circuit for said relay, 2. condition responsive element for closing said circuit, the resultant movement of said control unit from its starting position causing closure of said first switch, a safety switch in control of said electric device, means controlled by said control unit for opening said safety switch when said control unit reaches an intermediate position, means including a closed hot combustion switch for preventing such opening of the safety switch, switch means operated by said control unit for deenergizing said control motor when said control unit reaches a running position, a return switch for energizing said control motor independently of said switch means, means controlled by said relay upon deenergization thereof for closing said return switch, and means operated by said control unit when it reaches its starting position for opening said return switch, said first switch being opened by said control unit as it leave it rumiing position.

6. In a motor operated fuel burner control system, a control motor, a control unit operated thereby and having a starting position, an electric device which, when energized, causes the delivery of fuel to a burner, means for igniting the fuel delivered to th burner, a first switch in control of said electric device and said igniting means, said first switch being operated by said control unit and being open when said control unit is in its starting position, a relay in control of said control motor, a'circuit for said relay, a condition responsive element for closing said circuit, the resultant movement of said control unit from its starting position causing closure of said first switch, switch means operated by said control unit as it reaches a first intermediate position for deenergizing said igniting means, a safety switch in control of said electric device, means operated by said control unit as it reaches a second intermediate position for opening said safety switch, means including a closed hot combustion switch for preventing such opening of the safety switch, switch means operated by said control unit for deenergizing said control motor when said control unit reache a running position, a return switch forenergizing said control motor independently of said switch means, means controlled by said relay upon deenerglzation thereof for closing said return switch, and means operated by said control unit when it reaches its starting position for opening said return switch, said first switch being opened by said control unit as it leaves its running position.

7. In a motor operated fuel burner control system, a control motor, a control unit having a starting position, a running position, and an intermediate position operated thereby, a relay in control of said control motor for rotating said control unit successively from its starting p sition through its intermediate position, running position, and back to it starting position again, an electric device which, when energized, causes the delivery of fuel to a burner, a first switch for energizing said device, said first switch being closed by said control unit as it leaves its starting position and opened as it leaves it running position, a normally closed safety switch in con trol of said electric fuel feedin device, operating means for said safety switch, said means being biased to open switch position by said control unit when it is in its intermediate position, means operated by said relay when energized for preventing the opening of said safety switch, a condition responsive switch for energizing said relay for causing energization of said control motor, means operated by said control unit for deenergizing said relay to permit opening of said safety switch when said control unit reaches its intermediate position, and means including a closed hot combustion switch for maintaining energization of said relay to prevent opening of said safety switch if combustion is established first.

8. In a motor operated fuel burner control system, a control motor, a control unit having a starting position, a running position, and an intermediate position operated thereby, a relay in control of said control motor for rotating,

said control unit successively from its starting position through its intermediate position, running position, and back to its starting position again, an electric device which, when energized. causes the delivery of fuel to a burner, a first switch for energizing said device, said first switch being closed by said control unit as it leaves its starting position and opened as it leaves it running position, a normally closed safety switch in control of said electric fuel feeding device, operating means for said safety switch, said means being biased to open switch position by said control unit when it is in its intermediate position, means operated by said relay when energized for preventing the opening of said safety switch, a condition responsive switch for energizing said relay for causing energization of said control motor, means operated by said control unit for deenergizing said relay to permit opening of said safety switch when said control unit reaches its intermediate position, a return switch for energizing said control motor being closed by said safety switch operating means as said safety switch is being opened, means for opening said return switch as said control unit reaches its starting position, and means including a closed hot combustion switch for maintaining energization of said relay to prevent opening of said safety switch if combustion is established first.

9. In a motor operated fuel burner control system, a control motor, a control unit having a starting position, a running position, and an intermediate position operated thereby, a relay in control of said control motor for rotating said control unit successively from its starting position through its intermediate position, running position, and back to its starting position again, an electric devicejwhich, when energized, causes the delivery of fuelto a burner, a first switch for energizing said device, said first switch being closed by said control unit as it leaves its starting position and opened as it leaves its running position, a normally closed safety switch in control of said electric fuel feeding device, operating means for said safety switch, said means being biased to open switch position by said control unit when it is in its intermediate and running position, means operated by said relay when energized for preventing the opening of said safety switch, a condition responsive switch for energizing said relay for causing energization of said control motor, means operated by said control unit for deenergizing said relay to permit opening of said safety switch when said control unit reaches its intermediate position, means including a closed hot combustion switch for maintaining energization of saidrelay to prevent opening of said safety switch if combustion is established.

first, means operated by said control unit'deenergizing said control motor when said control unit reaches its running position, a return switch for energizing said control motor, said operating means closing said return switch upon deenergization of said relay by said condition responsive switch, and means for opening said return switch when said control unit reaches its starting posi tion, said control unit preventing said operating means from opening said safety switch except at its said intermediate position.

10. In a motor operated fuel burner control system, a control motor, a control unit having a starting position, a running position, and an intermediate position operated thereby, a relay in control of said control motor for rotating said control unit successively from its starting position through its intermediate position, running position, and back to its starting position again, an electric device which, when energized, causes the delivery of fuel to a burner, a first switch for energizing said device, said first switch being closed by said control unit as it leaves its starting position and opened as it leaves its running position, a normally closed safetyswitch in control of said electric fuel feeding device, operating means for said safety switch, said means being biased to open switch position by said control unit when it is in its intermediate and running position, means operated by said relay when energized for preventing the opening of said safety switch, a condition responsive switch forenergizing said relay for causing energization of said control motor, means operated by said control control motor when said control unit reaches its running position, a return switch for energizing said control motor, said operating means closing said return switch upon denergization of said relay by said condition responsive switch, and means for opening said return switch when said control unit preventing said operating means from opening said safety switch except at its said intermediate position.

11'. In a motor operated fuel burner control system, a control motor, a control unit having a starting position, a running position, and an intermediate position operated thereby, a relay in control of said control motor for rotating said control unit successively from its starting position through its intermediate position, running position, and back to its starting position again,

- an electric device which, when energized, causes the delivery of fuel to a burner, a first switch for energizing said device, said first switch being closed by said control unit as it leaves its starting position and opened as it leaves its running position, a normally closed safety switch in control of said electric fuel feeding device, a movable member for actuating said safety switch, said member being continuously biased to switch open position, said control unit cooperating with said movable member to prevent it from opening said safety switch except when said control unit is in its intermediate. position, an operating member having a first position in which it prevents said movable member from opening said safety switch and a second position in which it permits such action, said operating member normally assuming its first position, means operated by said control unit as it moves to its intermediate position for biasing said operating member for movement to its second position, means controlled by said relay when energized for preventing such movement, a condition responsiveswitch for energizing said relay for causing energization of said control motor, means operated by said control unit for deenergizing said relay to permit opening of said safety switch when said control unit reaches its intermediate positiomand means including a closed hot combustion switch for maintaining energization of said relay to'prevent opening of said safety switch if combustion is established first.

12. In a motor operated fuel burner control system, a control motor, a control unit having a starting position, a running position, and an intermediate position operated thereby, a relay in control of said control motor .for rotating said open position, said control unit cooperating with said movable member to prevent it from control unit reaches its starting position, said opening said safety switch except when said control unit is in its intermediate position, an operating member having a first position in which it prevents said movable member from opening said safety switch and a second position in which it permits such action, said operating member normally assuming its first position, means operated by said control unit as it moves to its intermediate position for biasing said operating member for movement to its second position, means controlled by said relay when energized for preventing such movement, a condition'responsive switch for energizing said relay for causing energization of said control motor, means operated by said control unit for deenergizing said relayto permit opening of said safety switch when said control unit reaches its intermediate position, a normally open return switch, means associated with said movable member for closing said return switch as it moves to its second position to permit opening of said safety switch whereby said control motor will be energized, means operated by said control unit as it reaches its starting position for opening said return switch, and means including a closed hot combustion switch for maintaining energization of said relay to prevent opening of said safety switch if combustion is established first.

13. In a motor operated fuel burner control system, a control motor, a control unit having a starting and a running position operated thereby, a relay in control of said control motor for rotating said control unit successively from its starting position through its running position and back to its starting positionagain, an electric device which, when energized, causes the delivery of fuel to a burner, a first switch for energizing said device, said first switch being closed by said control unit as it leaves its starting position and opened as it leaves its running position. a condition responsive switch for energizing'said relay for causing energization of said control motor, switch means operated by said control unit as it reaches its running position for deenergizing said control motor, a return switch, a movable member for closing said return switch, means controlled by said control unit for biasing said movable member to its switch closed position when said control unit is in its running position and switch open position when said control unit is in its starting position, means positioned by said relay for preventing movement of said movable member to its switch closed position when said relay is energized but permitting such movement when said relay is deenergized, means for holding said return switch in closed position once it has been closed by said movable member, and means operated by said'control unit when it reaches its starting position for releasing said holding means.

14. Ina motor operated fuel burner control system, a control motor, a control unit having a starting position, a running position and an intermediate position operated thereby, a relay in aeiaseo control of said control motor for rotating said control unit successively from. its starting position through its intermediate position, running position, and back to its starting position again,

an electric device which, when energized, causes the delivery of fuel to a burner, a first switch for energizing said device, said-first switch being closed by said control unit as it leaves its starting position and opened as it leaves its running position, a normally closed safety switch'in control of said electric fuel feeding device, a movable member ior actuating said safety switch, said-member being continuously biased to switch open position, said control unit cooperating with said movable member to prevent it from opening said safety switch except when said control unit is in its intermediate position, an operating member having a first position in which it prevents said movable member from opening said safety switch and a second position in which it permits such action, said operating member normally as-= suming its first position, means operated by said control unit as it moves to its intermediate and running position for biasing said operating member for movement to its second position, means controlled by said relay for preventing such movement when energized and permitting such movement when deenergized, a return switch for energizing said control motor independently of all other switches, said return switch being normally open, said operating member closing said return switch when it moves to its second position, means for holding said return switch closed once it has been closed by said operating member, means operated by said control for releasing said holding means when said control unit is in starting position, a condition responsive switch for energizing said relay for causing energization of said control motor, means operated by said control unit for deenergizing said relay to permit opening of said safety switch when said control unit reaches its intermediate position, means including a closed hot combustion swltch for maintaining energization of said relay to prevent opening of said safety switch if combustion is established first, and means operatd by said control unit for deenergizing said control motor when said control unit reaches running position.

' JOI-HI M. WILSON. 

